1. Field of the Invention
The present invention relates to a sensor element having a plurality of solid electrolytes each formed in the shape of a plate extending in a longitudinal direction, through holes penetrating the solid electrolytes in the thicknesswise direction, conductive layers respectively disposed in the through holes so as to form conduction paths, and insulating layers for electrically insulating each of the solid electrolytes and conductive layers. The present invention also relates to a method of manufacturing such a sensor element and to a gas sensor having such a sensor element.
2. Description of the Related Art
Conventionally, sensor elements are known which are formed by stacking a plurality of plate-shaped members (such as solid electrolyte substrates and insulating members) each formed in the shape of a plate extending in a longitudinal direction (JP-A-2001-242129 (FIG. 3 and the like)).
In such a sensor element, in order to electrically connect a first electrode portion disposed on the obverse surface side of the plate-shaped member and a second electrode portion disposed on the reverse surface side of the plate-shaped member, there are cases where a configuration is adopted in which the first electrode member and the second electrode member are electrically connected through a conductive layer disposed in a through hole penetrating the plate-shaped member in the thicknesswise direction.
In addition, the through hole is not limited to a through hole which penetrates a single plate-shaped member, and there are cases where a plurality of connected through holes penetrate a plurality of plate-shaped members. In the sensor element having such connected through holes, the conductive layers disposed in the interior of respective through holes form energizing paths penetrating the plurality of plate-shaped members in the thicknesswise direction (JP-A-9-105737 (FIG. 17 and the like)).
For example, as shown in FIG. 17 of the JP-A-9-105737, leads 12b and 13b of electrodes 12 and 13 of an oxygen sensor portion 3 are connected to terminals 78 by means of through holes 54 of a spacer 5 and through holes 77 of a substrate 80. Namely, through holes 54 and 77 are formed so as to penetrate the plurality of plate-shaped members (the spacer 5 and the substrate 80), and the conductive members disposed in the interiors of these through holes form energizing paths.
3. Problems to be Solved by the Invention
However, since the total thicknesswise dimension of the plate-shaped members is large, the depthwise dimension (lengthwise dimension) of the through hole which penetrates the plurality of plate-shaped members becomes large. Therefore, in cases where the internal conductive layers cannot be appropriately disposed, the energizing path constituted by a conductive layer is possibly broken (disconnected state).
In other words, in the through hole whose lengthwise dimension is large, the operation of inserting the conductive layer into its interior becomes difficult. Consequently, there are cases where the conductive layer becomes disconnected midway in the through hole at the time of inserting the conductive layer, resulting in a faulty energizing path (disconnected state).
Accordingly, the present invention has been devised in view of the above-described problems, and an object thereof is to provide a sensor element which has through holes penetrating the plurality of solid electrolytes in the thicknesswise direction and in which energizing paths formed by respective conductive layers disposed in the through holes are not prone to disconnection, as well as to a method of manufacturing the sensor element and a sensor including the sensor element.